You have exactly the right level of experience with the right firm & brand. Due to the consulting boom demand in the strat. consulting market in the UK is high especially for experienced consultants/ proj. managers. The window for this trend in the market may not last for more than a year, so moving now is the prudent decision. I don't think that lack of exposure to the UK market will be much of an issue at your level, unless you need to be selling work.